1. Field of the Invention (Technical Field):
The invention relates to apparatus for audio frequency equalization of multiple microphone sound systems, and a method for its use.
2. Background Art:
A sound system comprising multiple speakers and multiple microphones typically finds use in churches, conference rooms, meeting rooms, council chambers, and the like. Normally such spaces provide a poor acoustic match for the system loudspeakers employed therein. Accordingly, electronic equalization of loudspeaker response to provide more uniform system frequency response has long been utilized in sound system installation.
The problem of audio frequency equalization, however, exists with regard to microphones as well as loudspeakers. Broadly, audio frequency equalization and gain control of microphones has been accomplished by using manned audio mixing consoles or automatic microphone mixers. Manned consoles may employ a full-time operator to adjust both level and equalization of microphone channels to increase sound quality and eliminate feedback. These full-time manned systems are normally found in large audience capacity situations, for example, "live" concerts, and the like.
Sound systems without a full-time operator are normally found in smaller audience capacity situations, for example, the aforementioned council chambers, conference rooms, churches, and the like. Frequently, these sound systems employ part-time operators or automatic mixers that continuously adjust the level of each microphone channel, turning on only those channels in use. Further, most automatic mixers provide a logic output signal indicating the status (on or off) of each channel.
However, these mixers for smaller sound systems, whether manned part-time or automatic, cannot be fully optimized because microphone equalization is not available. Equalizers and filters may be patched into each microphone channel, but this solution is complex and relatively expensive.
U.S. Pat. No. 4,088,835 to Thurmond, et al., entitled Comprehensive Feedback Elimination System Employing Notch Filter, discloses a manual system capable only of producing a single equalization curve. Similarly, with U.S. Pat. No. 4,064,462, to Goehler, et al., entitled Acoustic Feedback Peak Elimination Unit; U.S. Pat. No. 4,091,236, to Chen, entitled Automatically Tunable Notch Filter and Method for Suppression of Acoustical Feedback; U.S. Pat. No. 4,079,199, to Patronis, Jr., entitled Acoustic Feedback Detector and Automatic Gain Control; and U.S. Pat. No. 4,165,445, to Brosow, entitles Circuit for Preventing Acoustic Feedback, all disclose circuitry wherein unwanted feedback detection and suppression operate by detecting the presence of a sustained frequency and subsequently either reducing system gain or tuning a notch filter to the unwanted frequency. U.S. Pat. No. 4,683,590, to Miyoshi, et al., entitled Inverse Control System, discloses an adaptive digital signal processing technique to modify frequency response to provide better performance; the system, however, is limited to a single equalization curve.